The present invention relates to a mounting method for core internals for mounting core internals such as a core shroud in a reactor pressure vessel received in a reactor building of a nuclear power plant, and more particularly to a mounting method for core internals suitable for use when core internals are replaced.
In the past, when the core shroud as core internals or the like is replaced, an old core shroud and old core internals such as a jet pump are cut and disassembled, and carried out, after which a new core shroud and new core internals such as a jet pump are individually carried into a reactor pressure vessel (hereinafter called xe2x80x9cRPVxe2x80x9d (Reactor Pressure Vessel), and they are mounted by welding or the like, as described in, for example, Japanese Patent Laid Open No. Hei 8 233972, Japanese Patent Laid Open No. Hei 8 152495, or Japanese Patent Laid Open No. Hei 10 132985. The shroud is carried-in in the form divided into two parts or singly, and the jet pump is singly carried-in in the form of a jet pump inlet mixer, a jet jump riser, and a jet pump diffuser.
Further, there has been known an integral construction of core internals such as a core shroud and a jet pump, as described in, for example, Japanese Patent Laid Open No. Hei 6 281776.
The core shroud is for output of 800 Mwe, and has a weight of about 40 tons, a diameter of about 5 m, and a length of about 7 m. In order to carry the core shroud into a reactor building operating floor through a large article carrying in hatch, there are a case of interfering with a dimension of the large article carrying in hatch and a case where the capacity of a ceiling crane in the reactor building is short. Therefore, it is necessary to divide and carry in them, as described in Japanese Patent Laid Open No. Hei 8 233972, Japanese Patent Laid Open No. Hei 8 152495, or Japanese Patent Laid Open No. Hei 10 132985, posing a problem that a term of work for replacing the core shroud becomes long.
Further, since with respect to the jet pump, its constituent parts, 20 jet pump inlet mixers, 10 jet pump risers, and 20 jet pump diffusers have been singly carried in, a worker moves into the core to assemble them, which requires measures such as installation of a core internals shield, thus posing a problem that a term of work for replacement becomes long.
That is, in the conventional systems described in Japanese Patent Laid Open No. Hei 8 233972, Japanese Patent Laid Open No. Hei 8 152495, or Japanese Patent Laid Open No. Hei 10 132985, there encountered a problem that a term of work for replacement of core internals is extended over a long period of time to lower the availability factor of a nuclear power plant.
On the other hand, in the method described in Japanese Patent Laid Open No. Hei 6 281776, the core internals such as a core shroud and a jet pump are formed into an integral construction, and the core internals are installed. However, the core internals described in Japanese Patent Laid Open No. Hei 6 281776 comprises a construction in which for example, as shown in FIG. 14 of the aforesaid Publication, a piston ring 55 is provided between an outer peripheral end of a baffle plate 18 mounted on the end of a core shroud 2 and a reactor pressure vessel 1, which requires to change the construction itself of the reactor pressure vessel. Accordingly, there encountered a problem not capable of applying to replacement of core internals of a reactor pressure vessel of the existing nuclear power plant which has been already installed and operated.
It is an object of the present invention to provide a mounting method for core internals capable of shortening a term of work for replacing core internals of a reactor pressure vessel of the existing nuclear power plant to enhance the availability factor of the nuclear power plant.
(1) For achieving the aforementioned object, according to the present invention, an integrated module of core internals having a new core shroud, a new jet pump and a new baffle plate is carried into a reactor pressure vessel in which an old baffle plate and an old shroud support welded and fixedly secured to the reactor pressure vessel, the new baffle plate being fixedly secured to the old baffle plate, the new core shroud being fixedly secured to the old shroud support.
With the method as described above, there is provided an integrated module having a new shroud, a new jet pump and a new baffle plate for replacement, and the module is carried into the reactor pressure vessel, and the new baffle plate is fixed secured onto the old baffle plate. Thus, carrying in is easy and processing for removing a distortion is unnecessary, thus enabling shortening of a term of work for replacement.
(2) In the above described configuration (1), preferably, the integrated module of the core internals having the new shroud, the new jet pump and the new baffle plate is carried into the reactor pressure vessel through an opening provided on a roof of a reactor building for receiving the reactor pressure vessel.
With the method as described, since the module is carried in from the opening on the roof of the reactor building, the carrying in of divided shrouds and the individual carrying in of constituent parts of a jet pump are unnecessary, thus being capable of shortening a term of work for replacing core internals.
(3) In the above described configuration (1), preferably, the new jet pump comprises a new jet pump inlet mixer, a new jet pump riser, and a new jet pump diffuser, the new jet pump diffuser having a lower end fixedly secured to the new baffle plate, the new jet pump riser being secured to the new shroud by a new jet pump riser brace mounted on an outer wall of the new shroud.
(4) For achieving the aforementioned object, according to the present invention, an old core shroud and an old jet pump from an old shroud support and an old baffle plate from a reactor pressure vessel are cut and carried out, and an integrated module of core internals having a new core shroud, a new jet pump and a new baffle plate is carried into a reactor pressure vessel in which an old baffle plate and an old shroud support welded and fixedly secured to the reactor pressure vessel are left, the new baffle plate being fixedly secured to the old baffle plate, the new core shroud being fixed secured to the old shroud support.
With the method as described above, it is possible to shorten a term of work for replacement.